David Cameron has apologised for employing Andy Coulson as his spin doctor, saying it was the "wrong decision".

Coulson, who has been convicted of phone hacking while he was working at the News of the World, was employed as Downing Street director of communications in May 2010, after he had resigned from the newspaper following the hacking scandal.

Mr Cameron said the former editor had given him "false assurances" he had no involvement in phone hacking and he had wanted to give him a "second chance".

The Prime Minister said he was given "undertakings by him on phone hacking and I always said if they turned out to be wrong I would make a full and frank apology and I do that today".

He said: "I am extremely sorry that I employed him. It was the wrong decision and I am very clear about that."

Image:Coulson arrives at the Old Bailey on Tuesday morning

Labour leader Ed Miliband said Mr Cameron needed to do more than just apologise and has "very, very serious questions to answer".

"This was not some small or accidental mistake - he stuck with Coulson over a long period of time and it wasn't like there wasn't information out there to arouse his suspicions - he was warned by the Deputy PM, he saw front page stories, he was warned by newspaper editors and yet still he refused to act and even today, defending some of the conduct of Coulson when he worked for him," Mr Miliband said.

Video:Cameron Apology For Coulson Job

"I think Cameron must do much more than an apology - he must give the country an explanation as to why he did not act, why he did not act on these allegations against Andy Coulson."

Mr Cameron insisted there had never been any complaints about the work Coulson did for him as leader of the opposition before he became Prime Minister or while he was working at Downing Street.

He said he and his chief of staff, Ed Llewellyn, had questioned Coulson on "whether he knew about phone hacking" but had been assured he had not.

Video:Osborne Challenged Over Coulson

Mr Cameron said: "But knowing what I now know, and know that the assurances were not right, it was obviously wrong to employ him. I gave someone a second chance and it turned out to be a bad decision."